The Bare (Board) Truth: Eliminate Confusion


Reading time ( words)

This column will address eliminating confusion that creates remakes both from the end-user/designer and the fabrication house. First, let’s talk about being clear about your intentions. What are some of the things that create miscommunication, lost time, and sometimes even remakes at the fabrication house of your choice? The first thing is querying the fabrication house for impedance numbers.

Let’s say you’ve asked for a material type on your drawing that is not either readily available or used by your fabricator. Here, you should expect the fabrication house to respond quickly and have all the deviations at once for you to review. This includes any impedance width changes, material types, or copper weights to produce the part. Any deviations regarding drawing notes such as wrap plate requirements that cannot be incorporated due to insufficient space or the extra etch compensation to meet the wrap plate requirement should also be addressed.

If your chosen fabricator comes back and says the material you have called out is not a standard stocked material for them, you are asking for a three-day turn. Giving you an alternative is great, but if by changing to the material they suggest your trace widths or spaces change to the point the part has to be laid out again, this can be very frustrating for the board designer.

To mitigate this from happening, give yourself and addition mil or two of space. This will allow the fabricator to resize the traces to meet your impedance and adjust dielectrics. For example, if you have designed the part as a 0.1-mm trace and space, this does not allow the fabricator to resize the traces without affecting the spaces. It may even require the fabricator to ask for a lighter starting copper weight to allow for a 0.5-mil change in trace width to still make the part producible.

This is where the etch compensation based on starting copper weight is key to remember when designing the part to allow for slight changes to either dielectric distance, starting copper weight, or trace width changes to meet your impedances. Having gone through all this, if the fabrication house does not state additional deviations due to the color of solder mask, material finish type, or even the material UL rating required, this is also frustrating for the designer. You should communicate with an engineering person at the fabrication house ahead of time to preclude these deviations from slowing down the part.

To read this entire column, which appeared in the February 2019 issue of Design007 Magazine, click here.

For more clarity in the design process, be sure to read and refer to Mark Thompson's "The Perfect Data Package," a concise book available at I-007eBooks.

Share

Print


Suggested Items

DFM 101: PCB Materials

04/30/2021 | Anaya Vardya, American Standard Circuits
One of the biggest challenges facing PCB designers is understanding the cost drivers in the PCB manufacturing process. This article is the first in a series that will discuss these cost drivers (from the PCB manufacturer’s perspective) and the design decisions that will impact product reliability.

Karen McConnell: Recipient of the IPC Raymond E. Pritchard Hall of Fame Award

03/11/2021 | Patty Goldman, I-Connect007
"I heard about IPC when I started a new job at UNISYS after graduating college. I moved from ASIC design to printed circuit boards," said Karen McConnell after being inducted into the Raymond E. Pritchard Hall of Fame. "At the time, in the late ’80s and early ’90s, there were rumors going around that printed circuit boards were going to disappear, and ASICs were going to take over the world. But something in printed circuit boards fascinated me. I minored in robotics in college as an electrical engineer and the data used to fabricate, assemble and test the boards is actually all robotic language. I was hooked."

Cadence’s Celsius: Don’t End up Holding the Hot Potato!

12/17/2020 | Clive "Max" Maxfield, Maxfield High-Tech Consulting
I was just thinking about the party game Hot Potato. It reminded me of today’s increasingly competitive marketplace: Accurate thermal analysis must be performed, and any potential issues have to be identified and addressed as early as possible in the design cycle. Otherwise the system will run into problems, market windows will be missed, and someone will be left holding the hot potato. Trust me, you do not want to be that someone.



Copyright © 2021 I-Connect007. All rights reserved.